Dolomite-magnesite refractory and batch therefor

ABSTRACT

Rebonded basic refractory consisting of 65-75% -4+65 mesh coarse grain bonded with -100 mesh (preferably at least 65% thereof being -325 mesh) magnesite fines. The coarse fraction in the batch is a mechanical mixture of (based on the whole batch) 1055% dead-burned magnesite and 15-60% fused dolomite (or equivalent mixed oxides). In the preferred embodiment, the two coarse materials are divided into each of two discrete particle size ranges, -4+12 mesh and -20+40 mesh; the former making up 45% of the batch and the latter 25% of the batch, with the fine deadburned magnesite being the remaining 30%. The ratio of fused grain to MgO in each of these two coarse fractions is preferably substantially the same as the ratio of fused grain to coarse MgO in the whole batch.

United States Patent 11 1 Doman Aug. 26, 1975 [75] Inventor: Robert C. Doman. Painted Post,

[73] Assignee: Corning Glass Works, Corning.

[22} Filed: May 13, 1974 [2]] Appl. No.: 469,117

Primary Examiner-J. Poer AIIUI'HL). Agent, or Firm-Barry S. Bissell; Richard N. Wardell; Clarence R. Patty. Jr.

[57] ABSTRACT Rebonded basic refractory consisting of 65-75% 4+65 mesh coarse grain bonded with l00 mesh (preferably at least 65% thereof being 325 mesh) magnesitc fines. The coarse fraction in the batch is a mechanical mixture of (based on the whole batch) 10-55% dead burned magnesite and l5-607 fused dolomite (or equivalent mixed oxides). In the preferred embodiment the two coarse materials are di' vided into each of two discrete particle size ranges. -4+l 2 mesh and 20+4(J mesh; the former making up 45% of the batch and the latter 25% of the batch, with the fine dead-burned magncsite being the remaining 3071. The ratio of fused grain to MgO in each of these two coarse fractions is preferably substantially the same as the ratio of fused grain to coarse MgO in the whole batch.

l4 Claims No Drawings DOLOMlTE-MAGNESITE REFRACTORY AND BATCH THEREFOR BACKGROUND OF THE INVENTION The invention pertains to improvements in chemically basic burned refractories of the dolomite type having as principal constituents Q and MgO. Refractories of this general type are recognized as suitable for forming the inside working linings of basic steelmaking furnaces or vessels where such linings must withstand the severe corrosive effects of the chemically basic slags. slag vapors. and other molten steelmaking ingre dients. More specifically. the invention pertains to rebonded dolomitic refractories comprising coarse fused dolomitic (dolomite with or without excess MgO or CaO. or equivalent oxides) refractory grain bonded with a fine fraction of magnesite (used in the art and herein synonymously with magnesia. both terms meaning a material with periclase as the stable crystal phase).

Various US. patents have dealt with such rebonded basic brick. in general. rebonding a coarse fraction of basic grain with a fine magnesite fraction is taught by the prior art. particularly US. Pat. Nos. 2.943.240 (Martinct). 3.060.042 (Leatham, et 111.). 3.262.795 (Davies. et al.). and 3.141.784 (King. et al.). It is the coarse fractions therein which distinguish the prior pa tents and also the present invention. Martinet teaches the use of a mechanical mixture of dead-burned dolomitic grain and dead-burned magnesite grain in his course fraction thereby obtaining a very dense compacted body. King discloses both a mechanical mixture and an intimately burned grain of dolomite and magnesite (the latter intimately burned grain is also disclosed by Leatham Lcatham discloses further that co-burned intimate mixtures of MgO and dolomite result in grain of greater usefulness in preparing rebonded brick than were mechanical mixtures of the separate constituents.

Davies grain is an improvement on the coarse grain of King. lt is Davies that discloses the use of the coarse grain in making compacted refractories bonded with fine MgO. and one infers that the grain of King and Leatham (referred to in Davies) could be fashioned into similar rebonded refractories. Davies coarse grain is a melted and resolidified intimate mixture of dolomite and magnesia subsequently crushed into discrete grain. Such grain is shown to have improved resistance to converter slags over the coburned grain of King.

SUMMARY OF THE INVENTlON Contrary to the trend and the teaching of the prior art (Leatham. Davies) toward using co-burned or cofused grain made from intimate mixtures of C210 and MgO as the coarse fraction in rebonded refractories. the present inventor has found. unexpectedly. that a mere mechanical mixture of coarse fused dolomitic (or equivalent oxide) grain, coarse dead-burned magnesite grain. and fine magnesite grain produces a compacted and burned refractory body of superior corrosion resistance to basic oxygen steelmaking slags.

Accordingly, the present invention is a size-graded particulate batch of magnesite and fused dolomite (or equivalent mixed oxides) and the compacted and burned refractories produced therefrom. The batch consists essentially of. on the weight basis. -35% of a fine fraction. substantially l 00 mesh and composed of dead-burned magnesite. and 65-75% of a coarse fraction. substantially -4+fi5 mesh and composed of a mixture of. based on the whole batch. 10-55% (preferably 20-40% dead-burned magnesite and 15-607 (preferably 30-5071) of a fused grain analyzing 50-6571 (110 and 30-45% MgO (preferably at least 98% MgO CaO) plus incidental impurities. Suitable commercially available calcined dolomites used by the inventor have produced fused grain within the more narrow range of 56-60% CaO and 40-44% MgO.

The fused grain in the coarse fraction is a melted. resolidified and crushed mixture of refractory raw materials with the proper chemical analysis. Preferably the fused grain is made using dolomite mineral or calcined or dead-burned dolomite as the raw material. Equivalent oxides of MgO and CaO may be substituted for the dolomite although at present this substitution would result in increased raw material cost.

The coarse fraction may be a continuously ground fraction with at least '7r of the material being -4+65 mesh particle size or the fraction may be subdivided into two discrete fractions (within the same 4+65 mesh limits) for a more dense compacted refractory body. The inventor prefers that the whole refractory batch be distributed. approximately.

45% -4+1 2 mesh coarse magnesite and coarse fused grain,

25% 20+40 mesh coarse magnesite and coarse fused grain. and

30% -l00 mesh fine magnesite.

The coarse dead-burned magnesite and coarse fused grain are preferably divided in each of the two coarse fractions in the same ratio as they are divided in the whole batch. The broad and preferred ranges for such a division are calculated (to the nearest 0.1% and tabulated in Table I. The preferred ranges appear in parentheses.

Mesh Size Fraction Fused Grain Dead-Burned MgO Sizes 9% of batch h of batch Z of batch Broad- Coarse 15-60 1 (1-55 4+65 65-75% (30-50) (20-40) Fine l00 25-3571 25-35 Preferred- 11.6-38.6 64-354 4+l2 45% (19.3-32.1) (12.9-25.7)

5.4-21A 3.h-19.6 20+4l) 25% (10.7-17.9) (Tl-14.3) l0t) 30% 30 DESCRIPTION OF THE PREFERRED EMBODIMENTS The calcined dolomite used consistently in the examples is a commercially available grade analyzing 57.8% CaO. 41.2% MgO. 0.5% SiO 0.2% Fe,();,, 0.15% Al- 3 .o with 0.15% 1.01.

EXAMPLE 1 A variety of commercial furnace bricks 4% inches X 4 tory and the volume of refractory eioded (determined by filling the eroded cavity with a measured volume of sand). The relative slag resistance is then observed by comparing each refractory result with the results of the 3 inches X 2% inches were mechanically pressed with other samples of the test run. The corrosion results on an impact press using 14 strokes at l0.000 psi per each refractory in a run may also be normalized to restrokc. After pressing, the bricks were placed in a gas duce the effect of dissimilar test runs when comparing oxygen furnace and fired to l600C. refractories from different runs. by recording results as The batches used in making the bricks and the slag a percent of the corrosion of a control refractory ineorrosion results are shown in Table I]. In addition to serted into the test cavity on each run. the dry ingredients. a 3'7( binder of paraffin wax was The slag composition in this example was 20% Fe(). mullered for minutes with the batch at 60C prior to 53.571 (110.21.57? SiO and 5.071 Al- O giving a limecompacting the brick. silica ratio of 2.5.

Composition ("4 Total Batch) Slag Data 4+l2 and 2()+4(l fractions Fired Bulk Max. Volume Example "/r Fused 7i Deadl0() mesh Dead- Density Cut Removed No. Dolomite Burned MgO Burned Mg() (71 (lbs/ft) (inchesl tin") 1 14 5t 30 17s 11.35 0.92 2 So 14 50 1x0 039 0.41 3 2s 42 30 179 0.54 0.57 4 42 2x 30 179 0.36 11.52 5 7 1 153 311 178 0.421 1.74 (1 e3 7 30 179 0 44 11.47

The fused grain was made from an electrically melted and resolidified batch of calcined dolomite analyzing EXAMPLE 2 57.8% CaO. 4|.27? MgO, 0.5% SiO.,, 0.2% Fe O;,, I 0.15% M 0 with 0.15% LOI. The melt was resolidi- 30 U SUbSmPIYIE -P dolfmlte fled by Casting on a graphite slab and the grain was gram 1n the coarse fraction for the fused dolomite of made therefrom by crushing and Sizing. In the exam, the present invention was investigated using the gram ples, the 4+l2 mesh particle fraction made up 45% of d'smbuuon Show" m luble the whole batch and the 20+40 mesh particle fraction made up of the whole batch. The quantities of (Z ol Batch fused dolomite and coarse dead-burned MgO were di- Mesh Sim q Dmnmiw Mgo vided into each of the two coarse fractions in the same ratio of fused grain to coarse MgO as in the whole xli batch. For example. Table III shows the division of ma- -100 30 terials for one preferred batch of Table II.

Bricks were pressed. burned and tested for slag resis- Partiele Distribution for the C izt$pzFrr1aLcstilon inzipaglenish tune: as in Example 1 i the results: Constituent $4 of Batch fraction fraction ("4 of batchl ('7' of batch] Hume or Refine Course g 42 27 5 Slag Cut tory Removed Fused 35'; Dead-Burned Dolomite 0.56 in. 0.72 inches 45 35 6502 MgO (35% Coarse MgOl "Ratio offoarsi: MgO to Fused Dolomite in the batch is l.5. 533 g U 43 Inches Typical analysis of the magnesite used throughout the examples herein was 98.5% MgO. 0.55% CaO. In addition to the superior corrosion resistance. the re- 0.387r SiO- and 0.44% others (Fe O A1 0 B 0 fractory with the fused dolomite grain showed less tenwith 0.13% LOI. Bulk density of the fine MgO fraction dency to fracture during thermal shock and more resisshould be at least 2.5-grams/cc for good corrosion resistance to hot face separation from the remainder of the tance. especially if the particle size is only l00 mesh. brick. The bulk density is not as important in the fine fraction EXAMPl E a if the l00 mesh MgO is reduced (by milling. etc.) to at least 657: -325 mesh. Comparisons of rebondcd brick using. as coarse frac- The slag test herein is a rather severe procedure detions. mechanical mixtures of dead-burned dolomite vised to determine the corrosion resistance of various plus dead-burned MgO (Sample l0). fused dolomite samples. In general. the particular slag under eonsiderplus dead-burned MgO (Sample I l J and fused doloation contacts. for a specified time period. a rotating mite plus fused Mgt) (Sample l2) were made after laboratory furnace cavity which is constructed from the s bricks were pressed. burned. and tested according to (1.

sample refractories. An electric arc maintains the slag at a normal temperature of about [750C Following the test run. the resistance of the samples is determined by measuring the depth of the slag cut into the refrac the procedures of Example I. Raw material batches were formulated as in the previous sample (Table IV), therefore mm 30% Mg() in the fine fraction in each sample.

Bulk Den-it Slag Cut olume Rctractory (tacking Hot '1' tlhsftt i tinehcsi ltcmmetl il|lCll\,\l Ruling Face Scicre Sample (ireen lll'L'Ll A Separation Separation Ill [77 IX (1-H 0.63 3.5 63 37 ll l7R l7) 0.37 1) Sn 2.4 (1 l1 I84 ITS (I46 (L73 IS 33 (I Sample ltl "l5" [)Ltld'BlH'llLtl Doloinlte -ofil Dead-Burned MgO Sample ll 3i; l-uscd Dolomite 65": Dead-Burned M110 Sample l2 '1 Fused Dolomite 35% I used MgO 30% Dead-Burned MgU Crack ratings are dimensionless values on a scale of 0-5 assigned to the type and size of crack formed during slag testing. The higher values indicate a greater de gree of cracking.

Hot face separation is a condition which resembles initial stages of spalling. In the furnace. a dense layer which hinders slag penetration is formed on the surface ofthe refractory exposed to the slag. This layer in some cases pulls away from the remainder of the refractory body and may be swept away by the contact of the slag or metal in the furnace. The percentage of refractories which showed this tendency is shown in Table V.

The refractory of the present invention (Sample 1 l showed superiority over the other two samples in corrosion resistance (despite a lower bulk density than Sample 10) and in tendency for hot face separation. although Sample l2 had slightly better cracking resis tance and adherence of the hot face.

EXAMPLE 4 Comparison of slag resistance revealed substantially equivalent results between refractories made according to the present invention and refractories replacing the coarse fraction of the present invention with similarly sized grain crushed from a fusion cast slab made from a batch of 7071 dolomite-30% MgO.

ln the foregoing specification. all mesh sizes are ae cording to the Tyler series and all percentages. unless otherwise noted. are on the weight basis.

I claim:

1. A size-graded particulate batch for the production of basic refractory bodies and consisting essentially of. with percentages on the weight basis.

25-357: substantially lO() Tyler mesh fine deadburned magnesitc.

lO-5571 substantially -4+6S Tyler mesh coarse dead-burned magnesite. and

l5-607r substantially -4+65 Tyler mesh coarse fused grain consisting essentially of. on the oxide basis. -65'71 CaO and 30-45% MgO.

2. The batch of claim 1 wherein the coarse fused grain is composed of a melted and resolidified raw material selected from dolomite. calcined dolomite and dead-burned dolomite.

3. The batch of claim 2 wherein the fused grain analyzcs, on the oxide basis. at least 9871 CaO plus MgO.

4. The batch of claim 1 in which the -4+65 Tyler mesh fraction consists of. based on the whole batch.

6.435.47r substantially 4+l2 Tyler mesh coarse dead-burned magnesite.

Jo-38.6% substantially 4+l2 Tyler mesh coarse fused grain.

Particle Distributions Sample 20 Sample Zl Using the batch formulation of Table VI the final compositions ofeach sample are fixed at 49% dolomite and 5 I71 MgO (normalized). However. in Sample 20. the dolomite and MgO in the coarse fraction have been fused together to produce a homogeneous mixture of CaO and MgO in discrete grain. To the contrary. Sample 2l. exemplary of the present invention. is a mere mechanical mixture of fused dolomite grain and deadburncd MgO. Both samples contain the 30% fine MgO bonding fraction.

Slag cut results for the two refractory Samples 20 and BI. made according to the procedure of Example I. were only 0.0] inch apart with Sample 20 showing the lesser cut of [L38 inches. The volume of refractory remmed during the slag test was identical at 0.48 cubic inches. No significant advantage can be seen lll .he corrosion data for Sample 20 which would warrant the additional cost of melting and rcsolidifying the MgO with the dolomite in the coarse fraction.

3.649.671 substantially 20+40 Tyler mesh coarse dead-burned magnesite.

5.42l.47( substantially 20+4O Tyler mesh coarse fused grain.

5. The batch of claim 4 wherein the 4+l2 Tyler mesh fraction makes up about 457: ofthe batch and the 20+4O Tyler mesh fraction makes up about 2571 of the batch.

6. The batch of claim 1 which consists essentially of 25-357: of the fine dead-burned magnesite. 20-40% of the coarse dead-burned magnesitc and 30-50% of the coarse fused grain. and wherein at least 7r of the fine dead-burned magnesite particles are -32S Tyler mesh.

7. The batch of claim 6 wherein the fused grain analyzes. on the oxide basis. at least 98']! CaO plug MgO.

8. The batch of claim 6 wherein the 4+65 Tyler mesh fraction consists of. based on the whole batch.

l2.9Z5.7' r substantially -4+l2 Tyler mesh coarse dead-burned magnesitc.

3 ,901 .72 l 7 8 93-321 uh l mi lly l3 'lyl r Wi tcriul selected from dolomite. calcined dolomite and fused grain. dead-burned dolomite. 71-14-30; Wmmmmll) :+4n 'l-ylcr mesh 1]. A compacted and burned refractory hody comdwd'humcd mugrlcmw posed essentially of the batch of claim I. [OJ-[79%. Subsmnuany 2O+4O Tyler mesh comm: l2. 'l'hc refractory body of claim ll which hLlS been med b a ri-- b mom 9. The batch of claim 8 wherein the 4+l2 Tyler mesh fraction makes up about 45% of the hatch and the A wmpdclcd and bumfid ltilcmry body com- +4() Tyler mesh fraction makes up about 2571 of Posed 9559mm! hatch hc butch l0 14. The refractory of claim [3 which has been 10. The batch of claim 9 wherein the coarse f d burned at a temperature of at least about l6()()C.

grain is composed of u melted and resolidifed raw mu- 

1. A SIZE-GRADED PARTICULATE BATCH FOR THE PRODCTION OF BASIC REFACTORY BODIES AND CONSISTING ESSENTIALLY OF, WITH PERCENTAGES ON THE WEIGHT BASIC, 25-35% SUBSTANTIALY -100 TYLER MESH FINE DEAD-BURNED MAGNESITE, 10-55% SUBSTANTIALLY-4165 TYLER MESH COARCE DEADBURNED MAGNESITE, AND 15-60% SUBSTANTIALLY-4+65 TYLER MESH COARSE FUSED GRAIN CONSISTING ESSENTIALLY OF, ON THE OXIDE BASIC, 50-65%CAO AND 30-45% MGO.
 2. The batch of claim 1 wherein the coarse fused grain is composed of a melted and resolidified raw material selected from dolomite, calcined dolomite and dead-burned dolomite.
 3. The batch of claim 2 wherein the fused grain analyzes, on the oxide basis, at least 98% CaO plus MgO.
 4. The batch of claim 1 in which the -4+65 Tyler mesh fraction consists of, based on the whole batch, 6.4-35.4% substantially -4+12 Tyler mesh coarse dead-burned magnesite, 9.6-38.6% substantially -4+12 Tyler mesh coarse fused grain, 3.6-19.6% substantially -20+40 Tyler mesh coarse dead-burned magnesite, 5.4-21.4% substantially -20+40 Tyler mesh coarse fused grain.
 5. The batch of claim 4 wherein the -4+12 Tyler mesh fraction makes up about 45% of the batch and the -20+40 Tyler mesh fraction makes up about 25% of the batch.
 6. The batch of claim 1 which consists essentially of 25-35% of the fine dead-burned magnesite, 20-40% of the coarse dead-burned magnesite and 30-50% of the coarse fused grain, and wherein at least 65% of the fine dead-burned magnesite particles are -325 Tyler mesh.
 7. The batch of claim 6 wherein the fused grain analyzes, on the oxidE basis, at least 98% CaO plug MgO.
 8. The batch of claim 6 wherein the -4+65 Tyler mesh fraction consists of, based on the whole batch, 12.9-25.7% substantially -4+12 Tyler mesh coarse dead-burned magnesite, 19.3-32.1% substantially -4+12 Tyler mesh coarse fused grain, 7.1-14.3% substantially -20+40 Tyler mesh coarse dead-burned magnesite, 10.7-17.9% substantially -20+40 Tyler mesh coarse fused grain.
 9. The batch of claim 8 wherein the -4+12 Tyler mesh fraction makes up about 45% of the batch and the -20+40 Tyler mesh fraction makes up about 25% of the batch.
 10. The batch of claim 9 wherein the coarse fused grain is composed of a melted and resolidifed raw material selected from dolomite, calcined dolomite, and dead-burned dolomite.
 11. A compacted and burned refractory body composed essentially of the batch of claim
 1. 12. The refractory body of claim 11 which has been burned at a temperature of at least about 1600*C.
 13. A compacted and burned refractory body composed essentially of the batch of claim
 8. 14. The refractory of claim 13 which has been burned at a temperature of at least about 1600*C. 